For years both the builders and users of continuous strip furnaces and other strip processing lines have been attempting to devise a better way of sealing both the inlet and/or outlet of this equipment. This invention relates to a method and apparatus for positively sealing the inlet and/or outlet of both vertical and horizontal continuous strip furnaces.
Conventional continuous strip furnaces are known to be equipped with air curtain type seals. Such seals have been found to be quite ineffective. As a result of the ineffective sealing which occurs on continuous strip furnaces which employ air curtain type seals, a number of problems and disadvantages are experienced.
It is desirable in conventional annealing furnaces to keep the annealing atmosphere relatively free from oxygen infiltration. It has been found that, as a result of ineffective sealing on conventional furnaces employing air curtain type seals, oxygen can readily infiltrate the annealing atmosphere. By having excess oxygen in the annealing atmosphere, the annealed product will fail to have the desirable bright finish. Thus the product will require a greater pickling time to produce the desired finish than would be required if the product was annealed in a relatively oxygen-free environment. Such a process suffers from the disadvantages of being time consuming and costly.
A further disadvantage resulting from ineffective sealing on conventional strip furnaces is the loss of heat which occurs. With the soaring costs and limited availability of energy producing fuels, it is extremely costly and undesirable to operate a strip furnace with ineffective sealing.
One technique for sealing an annealing furnace has been known for some time, however, it has been shown to have a number of disadvantages. This technique is illustrated in U.S. Pat. No. 890,314, to H. L. Thompson, wherein the inlet of the furnace is sealed by flap-type seals bearing against the metal strip which is to be treated.
Certain problems arise when sealing an annealing furnace in the manner exemplified by Thompson. Specifically, the particular location of the seals on the inlet of the furnace are such that the replacement of the seals is difficult since the seals are actually located inside the body of the furnace proper. A similar difficulty occurs on the outlet of the furnace, more specifically, the seal formed by flexible gates 20 and 21.